The Morrison government could face dozens of expensive legal cases as a result of its plans to transfer sick refugees and asylum seekers to Christmas Island instead of the Australian mainland, with lawyers and advocates confirming they are prepared to launch court action.

Prominent refugee lawyers said they were optimistic about the potential for legal challenges to overturn someone's detention on Christmas Island on the basis that the medical care available on the island is insufficient.

Immigration Minister David Coleman said on Wednesday the government would "ensure" adequate care was provided on the island, but could not say what that would require. The president of the island's council, Gordon Thomson, says the hospital had only six beds and that the island's own residents are frequently flown to Perth for treatment.

Human Rights Law Centre executive director Hugh de Kretser said the legal basis for a challenge would be that the government had breached its duty of care by sending refugees and asylum seekers to a place where inadequate treatment was available.

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"It’s something we’d look at if someone was transferred to Christmas Island with a particular medical need and there was medical evidence it couldn't be appropriately provided on Christmas Island," he said.

"It is certainly something that could be explored given that the reason someone would be brought to Australia is that they need medical care of a standard that they can’t get on Nauru or Manus Island."

George Newhouse, director of the National Justice Project, said it would be easier to mount a legal challenge for clients detained on Christmas Island than for those held offshore.

"It is my view that you could challenge the minister or department's decision to treat them on Christmas Island if there were not appropriate medical services available there," he said.

"As a lawyer based in Australia, it's obviously easier to proceed to court where your client is within the jurisdiction - you have Australian experts available to assess them or even see them, and I’m not in fear of being arrested or deported."

There are legal precedents for such cases, including numerous instances where the courts found Australia was in breach of its duty of care by holding people on Nauru or Manus Island despite their urgent medical needs.

Domestically, there have been cases where courts had ordered minors to be transferred out of remote immigration detention - such as the long-closed Woomera and Baxter centres - due to a lack of appropriate medical care.

Immigration Minister David Coleman said the government would ensure adequate medical treatment was available.Credit:Alex Ellinghausen

The government has estimated the cost of reopening Christmas Island at $1.4 billion over a number of years, including staff, charter flights to the island and medical services.

"We will ensure that adequate medical facilities are provided," Mr Coleman said Wednesday, though he did not detail how much that would cost or what it would involve.

Earlier this week, Labor leader Bill Shorten said it was "fine" if refugees received medical treatment on Christmas Island, as long as it was of an adequate standard it worked.

Shadow foreign minister Penny Wong echoed that position on Wednesday. "What we want is for them to get the medical care they need, wherever that may be," she said.

Department of Home Affairs secretary Michael Pezzullo revealed at Senate estimates it was the government's policy to send any refugees and asylum seekers transferred under that law to Christmas Island in the first instance, unless there were extenuating circumstances.

The Greens and independent MP Kerryn Phelps have accused the government of betraying the will of the Parliament, which passed the refugee treatment bill last week against the wishes of the government.

On Tuesday, Home Affairs Minister Peter Dutton predicted legal challenges. "That's the reality, and there will be Federal Court action as there always is in this space," he said.

"There will be cases taken to the Federal Court almost straight away in my judgment. There's a lot of pro-bono legal work that takes place in this space and it will happen again no doubt."